1. Field of the Invention
The invention relates to a method of manufacturing a Bitter type coil, entering more particularly into the construction of a large sized magnet able to be used in a nuclear magnetic resonance (NMR) image forming installation. The invention also relates to a solenoid magnet having at least one Bitter type coil constructed by using this method.
2. Description of the Prior Art
It is known that NMR image forming installations require a large sized magnet capable of generating a uniform magnetic field in a given region of space. Typically, it is necessary to generate a magnetic field of 0.15 to 0.5 teslas with a homogeneity of 1 to 10 parts per million (ppm) in a sphere having a diameter of 40 cm at least.
Furthermore, Bitter coils are well known for producing intense magnetic fields. The structure proposed by Bitter is a winding formed of metal annular disks (generally made from copper or aluminium) split so as to form as many turns and connected so as to define a substantially helical winding with flat turns. The stack of disks is held in position by a plurality of tie rods. This structure is advantageous for it allows efficient cooling of the magnet, by forming holes in the disks (and in the insulators separating these disks). These holes are disposed in the same configuration from one disk to another so as to form a set of channels parallel to the axis of the coil. A cooling fluid, for example deionized water, kerosene or oil, flows in the channels.
It is possible to calculate a magnet delivering a magnetic field of required homogeneity in a certain volume in the vicinity of its center of symmetry and formed of a number of such Bitter coils arranged along a common longitudinal axis. Methods of calculating such magnets are for example explained in other patent applications of the applicant.